There exists different multiple access modes, such as code division multiple access (CDMA), frequency division multiple access (FDMA) and time division multiple access (TDMA), in wireless communication system. With the development of wireless communication technologies, new modes of multiple access including space division multiple access (SDMA) and orthogonal frequency division multiple access (OFDMA), are emerging continuously.
Each multiple access mode has its own features. For example, FDMA technology divides the total bandwidth of a system into several non-overlapped sub-bands, each of which is allocated to a user. TDMA technology divides each channel into several time slots, each of which is allocated to a user. CDMA technology allocates to each user a pseudo random code with good auto-correlation and cross-correlation property. As such, multiple users can simultaneously send signal in the same bandwidth. TDMA and CDMA generally use FDMA to divide their frequency band into smaller frequency bands, and then perform time division operation or code division operation. SDMA utilizes space irrelevance to obtain multiple access capability.
As for these traditional modes of multiple access, since a base station and a terminal send signals with a single carrier frequency or on a narrow band, it is more suitable for supporting low-speed voice services. For high-speed data services, there is relatively severe inter-symbol interference in a single carrier frequency system or narrowband system, thus the requirement for the equalizer of receiver is higher. For those multiple access techniques that support conventional multi-carrier, they need to use filter banks to separate signals at the receiver side. This kind of multiple access techniques are comparatively simple to implement, however, they have the disadvantage of low spectrum efficiency.
OFDMA, which supports high-speed data service, divides a channel band into different sub-channels, and multiple users can simultaneously send signals on different sub-channels. An OFDMA system can effectively reduce inter-signal interference through serial-parallel conversion of high-speed data, thus to reduce the complexity of the receiver. Moreover, the OFDMA system utilizes orthogonality between the sub-carries to allow the spectrum of the sub-channels to overlap with each other, so that the usage of spectrum resource can be maximized. Compared with a single carrier system, however, the OFDMA system has relatively higher peak-to-average power ratio.
With the development of wireless communication technology, especially with the development of multiple access techniques, categories of the wireless terminals and services supported are also greatly enriched. In addition to all kinds of handheld terminals, fixed terminals as well as the application of notebook computers are also an important part. Basically, because of their size and cost, the handheld terminals require relatively small power consumption, thus traditional single-carrier multiple access techniques such as SC-FDMA (single carrier frequency division multiple access) may be applied to support low-speed voice service. The fixed terminals and notebook computers can use power supply or other stable power equipment, thus they are able to provide users with high-speed data service and as a result, the multiple access mode of OFDMA can be applied.
In the present wireless communication system, a base station can only support terminals with a single multiple access mode. For example, in a CDMA communication system, a base station only supports the terminals whose uplink and downlink both apply CDMA technology. In an IEEE (Institute of Electrical and Electronics Engineers) 802.16e system, a base station only supports the terminals whose uplink and downlink both apply OFDMA technology.
However, with the development of wireless communication technologies, for different modes of multiple access, there is an increasing need for a communication system that is capable of supporting different multiple access modes with the same carrier frequency.